Heretofore, a diesel engine (hereafter referred to as "engine") has been equipped with an apparatus, such as a turbocharger or a mechanical turbocharger, which increases the volume of intake air and expands the exhaust gas output. A pneumatic governor is used which can control the volume of fuel supplied to the engine by the pressure supplied by the volume of intake air, which can prevent the engine from stopping, and which can control a maximum rotational speed. Furthermore, the temperature of the engine exhaust gas is measured, that exhaust gas temperature is compared to a corresponding threshold value, and the presence or absence of one of the following abnormalities in the engine is detected:
(1) an open/close abnormality of valves such that the exhaust gas from the exhaust process flows from the intake valve to the intake side; PA1 (2) a breakdown of the turbocharger such that the temperature of the exhaust gas rises; or PA1 (3) a breakdown of fuel injection devices such that the volume of injected fuel increases and the temperature of the exhaust gas rises.
Periodically, or when an abnormality is thought to have occurred, the operator measures the pressure of the blowby gas in the engine to detect an abnormality such as wear of the pistons or the piston rings. In the same way, the pressure and temperature of the engine lubrication oil are measured, and the presence or absence of an abnormality in a pump, a valve, a pressure regulator, or another component is detected; or the air intake pressure is measured and the presence or absence of clogged filters is detected.
Simply measuring a specific operating variable (for example, the exhaust gas temperature) of the engine systems, such as the fuel system, the lubrication system, the cooling system, the intake system, and the exhaust system, and comparing the value of the specific operating variable with a corresponding threshold value can result in the detection of an abnormality when the value of the specific operating variable clearly surpasses the corresponding threshold value. However, if the value of the specific operating variable is near to and lower than the corresponding threshold value, an erroneous judgment that no abnormality is present may occur, resulting in damage to the engine. Setting the corresponding threshold value slightly low, to be on the safe side, causes a problem in that an abnormality judgment can be made even when there is no abnormality, resulting in needless inspections being conducted and wasted man hours.
Furthermore, if the specific operating variables are to be measured at certain intervals, even when no load is applied and hence breakdowns are unlikely to occur, or at low rotational speeds, and the values of the specific operating variables are corrected and compared with the corresponding threshold values, a computer with a large storage capacity is required, and costs rise. If multiple computers are used, a problem arises in that the control becomes complex and the control speed is slower.
Moreover, even if the operator measures the values of the specific operating variables of the engine (for example, the blowby gas pressure) at periodic intervals, or when an abnormality is thought to have occurred, a problem results in that while the circumstances at that particular time can be judged, it is not possible to ascertain kinetic changes which take place over time, e.g., in the wear of the pistons or the piston rings, because changes which take place with the passage of time are not being measured; thus, an accurate judgment cannot be made. Furthermore, a problem results in that, because conditions, such as the engine output, are not consistent when the specific operating variable is measured, it is impossible to make an accurate judgment.